1. Field of the Invention
The present invention relates to a scroll compressor, in particular, one suitable for operation in a vapor-compression refrigerating cycle which uses a refrigerant, such as CO2, in a supercritical area thereof.
2. Description of the Related Art
As for the vapor-compression refrigerating cycle, one of the recently proposed measures to avoid the use of Freon (from a refrigerant) in order to protect the environment is the use of a refrigerating cycle using CO2 as the working gas (i.e., the refrigerant gas). This cycle is called xe2x80x9cCO2 cyclexe2x80x9d below. An example thereof is disclosed in Japanese Examined Patent Application, Second Publication, No. Hei 7-18602. The operation of this CO2 cycle is similar to the operation of a conventional vapor-compression refrigerating cycle using Freon. That is, as shown by the cycle Axe2x86x92Bxe2x86x92Cxe2x86x92Dxe2x86x92A in FIG. 5 (which shows a CO2 Mollier chart), CO2 in the gas phase is compressed using a compressor (Axe2x86x92B), and this hot and compressed CO2 in the gas phase is cooled using a gas cooler (Bxe2x86x92C). This cooled gas is further decompressed using a decompressor Cxe2x86x92D), and CO2 in the gas-liquid phase is then vaporized (Dxe2x86x92A), so that latent heat with respect to the evaporation is taken from an external fluid such as air, thereby cooling the external fluid.
The critical temperature of CO2 is approximately 31xc2x0 C., that is, lower than that of Freon, the conventional refrigerant. Therefore, when the temperature of the outside air is high in the summer season or the like, the temperature of CO2 at the gas cooler side is higher than the critical temperature of CO2. Therefore, in this case, CO2 is not condensed at the outlet side of the gas cooler (that is, line segment B-C in FIG. 3 does not intersect with the saturated liquid curve SL). In addition, the condition at the outlet side of the gas cooler (corresponding to point C in FIG. 3) depends on the discharge pressure of the compressor and the CO2 temperature at the outlet side of the gas cooler, and this CO2 temperature at the outlet side depends on the discharge ability of the gas cooler and the outside temperature (which cannot be controlled). Therefore, substantially, the CO2 temperature at the outlet side of the gas cooler cannot be controlled. Accordingly, the condition at the outlet side of the gas cooler (i.e., point C) can be controlled by controlling the discharge pressure of the compressor (i.e., the pressure at the outlet side of the gas cooler). That is, in order to keep sufficient cooling ability (i.e., enthalpy difference) when the temperature of the outside air is high in the summer season or the like, higher pressure at the outlet side of the gas cooler is necessary as shown in the cycle Exe2x86x92Fxe2x86x92Gxe2x86x92Hxe2x86x92E in FIG. 3. In order to satisfy this condition, the operating pressure of the compressor must be higher in comparison with the conventional refrigerating cycle using Freon. In an example of an air conditioner used in a vehicle, the operating pressure of the compressor is 3 kg/cm2 in case of using R134 (i.e., conventional Freon), but 40 kg/cm2 in case of CO2. In addition, the operation stopping pressure of the compressor of this example is 15 kg/cm2 in case of using R134, but 100 kg/cm2 in case of CO2.
Here, a general scroll compressor comprises a casing; a fixed scroll and a revolving scroll in the housing, each scroll comprising an end plate and a spiral protrusion built on an inner surface of the end plate, said inner surface facing the other end plate so as to engage the protrusions of each scroll and form a spiral compression chamber. In this structure, the introduced working gas is compressed in the compression chamber and then discharged according to the revolution of the revolving scroll. In such a scroll compressor using CO2 as the working gas and having high operating pressure, the back face of the revolving scroll is supported using a thrust ball bearing so as to put up with or stand up to large thrust imposed on the revolving scroll, so that leakage of the working gas from the compression chamber is prevented as much as possible. As an example, Japanese Unexamined Patent Application, First Publication, Hei 3-54387 discloses supporting the back face of the revolving scroll by using a thrust board and to form a concave portion in a contact face between the thrust board and the revolving scroll so as to seal the relevant part from oil or water. As another example, Japanese Examined Patent Application, Second Publication, Hei 1-44911 discloses the provision of a back pressure chamber at the back face side of the revolving scroll and support of the back face of the revolving scroll by using a piston forced by a spring.
The structure for supporting the revolving scroll using a thrust ball bearing has the following problems: (i) loud noise is generated, and (ii) it is necessary to use a thrust ball bearing having a large diameter so as to secure a sufficiently long life; thus, it is difficult to manufacture a smaller scroll compressor. In addition, in the structure in which the revolving scroll is simply supported using a thrust board, sufficient effect of decreasing thrust loss cannot be obtained.
In consideration of the above circumstances, the inventors of the present invention diligently continued to research, and discovered that the thrust load can be effectively decreased, preferable lubricating effects can be obtained, and a smaller scroll compressor can be realized without degrading the compression efficiency, based on a simple arrangement such that a high-pressure oil or working gas is introduced from an external supply towards a face (of the thrust board) which faces the revolving scroll. Accordingly, an objective of the present invention is to provide a scroll compressor for effectively decreasing the thrust load imposed on the revolving scroll and improving the mechanical efficiency without degrading the compression efficiency, thereby realizing a simpler and smaller scroll compressor whose maintenance can be easily performed. Therefore, the present invention provides a scroll compressor comprising:
a casing;
a fixed scroll provided in the housing and comprising an end plate and a spiral protrusion built on one face of the end plate; and
a revolving scroll provided in the casing and comprising an end plate and a spiral protrusion built on one face of the end plate, wherein the spiral protrusions of each scroll are engaged with each other so as to form a spiral compression chamber, wherein:
an introduced working gas is compressed in the compression chamber and then discharged according to the revolution of the revolving scroll;
a thrust member for thrust-supporting the end plate of the revolving scroll is provided at the back-face side of the end plate of the revolving scroll;
a pressure pocket is formed in a face of one of the thrust member and the end plate of the revolving scroll, wherein said face faces the other of the thrust member and the end plate of the revolving scroll; and
a high-pressure introduction hole for introducing a high-pressure fluid into the pressure pocket is provided at one of the thrust member side and the revolving scroll side.
According to the above structure, the high-pressure oil or working gas can be supplied as the high-pressure fluid via an oil supply path and an oil introduction hole (i.e., the high-pressure introduction hole), thereby decreasing the thrust load of the revolving scroll. Therefore, it is possible to prevent noises, and the thrust load imposed on the revolving scroll can be decreased by using the high-pressure fluid for a long period of time, thereby decreasing the mechanical loss. In addition, the scroll compressor according to the present invention can have a simpler structure in comparison with conventional scroll compressors. Thus, the maintenance can be easily performed and a smaller body can be realized.
In order to supply the high-pressure fluid to the pressure pocket, it is possible that a fluid path is formed in the casing; the high-pressure introduction hole is formed in the thrust member, where one end opens and joins the pressure pocket and the other end opens and joins the fluid path in the casing; and a high-pressure fluid is supplied from the compression chamber via the fluid path and the high-pressure introduction hole to the pressure pocket.
In a specific example, a high-pressure fluid supply means is provided for supplying the high-pressure fluid to the fluid path, where the supply means comprises an oil separator for lubricating oil from the discharged high-pressure working gas, and return piping for returning the lubricating oil separated by the oil separator to the fluid path. In this case, the high-pressure oil can be reused.
In another specific example, the high-pressure introduction hole is formed in the end plate of the revolving scroll, where one end opens and joins the pressure pocket and the other end opens and joins the compression chamber; and the working gas in the compression chamber is supplied as a high-pressure fluid via the high-pressure introduction hole to the pressure pocket. Accordingly, the high-pressure fluid in the compression chamber can be supplied to the pressure pocket.
In another specific example, the high-pressure introduction hole is formed in the end plate of the revolving scroll, where one end opens and joins the pressure pocket and the other end opens and joins the compression chamber; and a plurality of compression chambers are provided by engaging the fixed scroll and the revolving scroll, and working gases having different pressures in the compression chambers are supplied as a high-pressure fluid via the high-pressure introduction hole to the pressure pocket. In order to introduce working gases of different pressures to the pressure pocket, a plurality of high-pressure introduction holes may be provided, or a single high-pressure introduction hole may be ramified to form branch holes. Accordingly, preferably combined working gases having different pressures can be introduced into the pressure pocket.
Preferably, the working gas is carbon dioxide. In this case, the present invention can be effectively applied to a scroll compressor which uses a refrigerating cycle using CO2 as the working gas, and which has a high operating pressure.